Metal working shops and plants commonly use devices referred to as "collet fixtures" for holding bar stock on machine beds or tables as the workpieces are machined by such operations as milling, drilling, tapping and grinding. Most of these collet fixtures have a workpiece clamping and engaging element called a "5C Collet" which is a collet similar to those found in milling machine spindles for holding and clamping milling tools except the 5C Collets are externally threaded rather than internally threaded as in the milling tool collets.
The 5C Collet is conventionally machined from round bar stock and includes a central through bore, a single diameter shank portion with a threaded end, and a frusto-conical portion at the opposite end having a plurality of slots milled radially therethrough that extend through to the central bore. As the resulting frusto-conical segments are cammed by some external taper, they flex inwardly grasping the cylindrical bar stock workpiece thereby holding it firmly in position.
There are generally two types of collet fixtures presently popular in the machine tool industry, one that includes an axially fixed 5C Collet that utilizes a movable member for camming the collet closed, and one that utilizes a movable collet that engages a stationary camming surface for causing the collet to close. In both cases, however, these collet fixtures include a supporting frame that must be aligned, referenced, and clamped and bolted to the machine bed, whether it be a drilling machine, a tapping machine or a grinding machine.
One such collet fixture is the Yuasa collet fixture having a Rutland Tool and Supply Co., Inc.(City of Industry, California), Part No. 2411-5360(1994). This collet fixture includes a cast iron rectangular base that is bolted to the machine bed carrying a plurality of sleeves and nuts that surround a collet for holding the workpiece in position. A lever action indexing handle permits these sleeves and rings to be rotated so that the workpiece can be machined at various angles. The collet slides inside this type of fixture. It is held in place by an adjusting nut. Rotation of the sleeve assembly is controlled by the use of a key in the fixture and a key way in the collet. As the fixture mechanism is actuated, the collet is drawn into an internal taper. As pressure increases, the taper in the fixture forces the taper on the collet to collapse, closing the inside of the collet. In this style of fixture, the collet moves until the workpieces clamps. The smaller the workpiece, the farther the collet must travel to achieve its goal. Until clamping occurs, both the collet and the work move together. If the work varies in size, the position of the work in its set-up varies proportionately. Controlling the work size may be required for an efficient set-up.
The second type of collet fixture commonly found in the industry utilizes a fixed collet actuated by a movable sleeve. One such collet fixture is referred to as a horizontal and vertical 5C Collet fixture, Part No. 2404-0005 also sold by Rutland Tool and Supply. This fixture utilizes a sleeve with an inside taper matching that on the collet. The collet is held in place in the fixture by an adjusting nut. As the fixture mechanism is actuated, the sleeve moves rather than the collet. The taper in the sleeve is forced into the taper on the collet. The collet responds by collapsing until it firmly embraces the workpiece. The smaller the workpiece, the farther the sleeve must travel to fully engage the collet. Since the collet does not move, the size of the work does not effect the position of the work. The disadvantage to this style is that it does not allow the use of step chucks.
The disadvantage in both of these types of collet fixtures is that they require very accurate set-up and clamping to the machine bed or table before they can be utilized.
There have also been provided in the past collet block checks that are essentially tapered sleeves that can be clamped in a vise that are designed to receive 5C Collets. These essentially are simply square blocks with a collet receiving opening therethrough or hexagonal blocks, both of which are clamped directly in the machine vise. These block chucks require alignment in the vise with respect to the machining axis or axes in the same way that the collet fixtures do, and they also lack the structural integrity required for many machining operations. Also clamping and unclamping occurs either by tightening a nut on the collet with a spanner wrench or via a small cam actuating lever. The latter lacks strength and rigidity and the spanner wrench consumes valuable production time.
It is a primary object of the present invention to ameliorate the problems noted above in 5C Collet fixtures.